04-04-2017, 11:11 PM
seminar report on jet propulsion............
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seminar report on jet propulsion
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seminar report on jet propulsion............
13-04-2017, 10:07 AM
Jet propulsion is the thrust produced by passing a jet of matter (typically air or water) in the direction opposite to the direction of movement. According to Newton's third law, the movable body is propelled in the opposite direction to the jet. It is most commonly used in the jet engine, but it is also the most common means of spacecraft propulsion. Several animals, including cephalopods, sea hares, arthropods and fish, have developed evolutionarily jet propulsion mechanisms. Jet propulsion is most effective when the Reynolds number is high, ie the object being propelled is relatively large and passes through a medium of low viscosity.
Jet propulsion revolutionized the science of flight by dramatically increasing possible speeds and altitudes, thus enabling space exploration. The term "jet propulsion" refers to the action produced by a reactor upon the expulsion of matter. For example, when matter in a typical rocket (such as gunpowder in fireworks) is lit, the resulting chemical reaction produces heat and gases, which escape from the rocket and push it forward. The oxygen required for combustion is carried (in tanks or in combined form) on the rocket itself so that the thrust of the rocket is independent of the atmosphere. Other jet propulsion devices depend on the air introduced into the engine to supply the required oxygen. After the heat is released by combustion, the hot gases are accelerated through the engine so that the output velocity is greater than the velocity of the air stream at the inlet.
![[Image: 000D485C-781F-1C72-9EB7809EC588F2D7_arch1.gif]](https://www.scientificamerican.com/media/inline/000D485C-781F-1C72-9EB7809EC588F2D7_arch1.gif)
In both autonomous rocket motors and air-jet power units, the thrust that can be generated is proportional to the mass of material ejected from the unit in a given time, as well as the increase in mass velocity with Respect to unity. Therefore, the same forward pushing force can occur in two ways: by pushing back a large mass of material at low speed for a given period of time (as in turbofan engines) or by ejecting a smaller mass of material at greater Speed (as in turbojet and shuttle engines). The two sources of mass are the propellant, or fuel, and the oxidant, or air.
![[Image: 000D485C-781F-1C72-9EB7809EC588F2D7_arch2.gif]](https://www.scientificamerican.com/media/inline/000D485C-781F-1C72-9EB7809EC588F2D7_arch2.gif)
Fuels contain a large amount of potential energy, which is rapidly released during combustion. A portion of this thermal energy becomes useful work, moving the vehicle through the atmosphere or into space. However, another part, in the form of kinetic energy of the jet, is lost and dissipates in the atmosphere. The highly fuel-efficient turbofan engines used in modern commercial aircraft engines try to minimize this latter portion. To do this, they impart a moderate increase in mass velocity to the combustion products for the large mass of air sucked through the engine at a given time. However, turbojet and shuttle engines, which meet the most demanding supersonic flight requirements, are less fuel efficient.
Several types of jet engines have been developed to provide the thrust and engine performance required for a wide range of flight altitudes and speeds. The turbojet engines, turbo-propeller and compressed air piston operate according to similar principles in that they increase the air pressure induced before combustion and expand high-energy gases before they exit, into a nozzle or exhaust system . In turbojet engines, the induced air passes through a compressor to increase its pressure before entering the combustor, then through a turbine before accelerating into the exhaust nozzle. The piston motor, however, has no moving parts; It produces an increase in the piston pressure from the deceleration of high-velocity induced air in the intake diffuser. The water jet engine can only operate at supersonic speeds and therefore requires another launching device, such as a rocket or a turbojet engine, to accelerate it at the required speed.
![[Image: 000D485C-781F-1C72-9EB7809EC588F2D7_arch3.gif]](https://www.scientificamerican.com/media/inline/000D485C-781F-1C72-9EB7809EC588F2D7_arch3.gif)
Above a certain height atmospheric density decreases and jet propulsion is only possible for rocket engines carrying their own oxygen. Rocket engines use solid or liquid fuels. Solid rockets are the oldest types, and their bodies contain the combustion chamber and the solid fuel is mixed with the oxidant. When the fuel is turned on, the gaseous combustion products are accelerated through the nozzle to produce thrust. In liquid rockets, fuel and oxygen are stored in separate tanks and fed at controlled speeds into the combustion chamber.
Jet propulsion revolutionized the science of flight by dramatically increasing possible speeds and altitudes, thus enabling space exploration. The term "jet propulsion" refers to the action produced by a reactor upon the expulsion of matter. For example, when matter in a typical rocket (such as gunpowder in fireworks) is lit, the resulting chemical reaction produces heat and gases, which escape from the rocket and push it forward. The oxygen required for combustion is carried (in tanks or in combined form) on the rocket itself so that the thrust of the rocket is independent of the atmosphere. Other jet propulsion devices depend on the air introduced into the engine to supply the required oxygen. After the heat is released by combustion, the hot gases are accelerated through the engine so that the output velocity is greater than the velocity of the air stream at the inlet.
In both autonomous rocket motors and air-jet power units, the thrust that can be generated is proportional to the mass of material ejected from the unit in a given time, as well as the increase in mass velocity with Respect to unity. Therefore, the same forward pushing force can occur in two ways: by pushing back a large mass of material at low speed for a given period of time (as in turbofan engines) or by ejecting a smaller mass of material at greater Speed (as in turbojet and shuttle engines). The two sources of mass are the propellant, or fuel, and the oxidant, or air.
Fuels contain a large amount of potential energy, which is rapidly released during combustion. A portion of this thermal energy becomes useful work, moving the vehicle through the atmosphere or into space. However, another part, in the form of kinetic energy of the jet, is lost and dissipates in the atmosphere. The highly fuel-efficient turbofan engines used in modern commercial aircraft engines try to minimize this latter portion. To do this, they impart a moderate increase in mass velocity to the combustion products for the large mass of air sucked through the engine at a given time. However, turbojet and shuttle engines, which meet the most demanding supersonic flight requirements, are less fuel efficient.
Several types of jet engines have been developed to provide the thrust and engine performance required for a wide range of flight altitudes and speeds. The turbojet engines, turbo-propeller and compressed air piston operate according to similar principles in that they increase the air pressure induced before combustion and expand high-energy gases before they exit, into a nozzle or exhaust system . In turbojet engines, the induced air passes through a compressor to increase its pressure before entering the combustor, then through a turbine before accelerating into the exhaust nozzle. The piston motor, however, has no moving parts; It produces an increase in the piston pressure from the deceleration of high-velocity induced air in the intake diffuser. The water jet engine can only operate at supersonic speeds and therefore requires another launching device, such as a rocket or a turbojet engine, to accelerate it at the required speed.
Above a certain height atmospheric density decreases and jet propulsion is only possible for rocket engines carrying their own oxygen. Rocket engines use solid or liquid fuels. Solid rockets are the oldest types, and their bodies contain the combustion chamber and the solid fuel is mixed with the oxidant. When the fuel is turned on, the gaseous combustion products are accelerated through the nozzle to produce thrust. In liquid rockets, fuel and oxygen are stored in separate tanks and fed at controlled speeds into the combustion chamber.
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